How are professional transmission lines and levels different from consumer lines and levels? What is -10 and +4? Whats a balanced or differential line?
Professional transmission lines differ from consumer lines in two ways. First, consumer lines tend to run about 14 dB lower in level than pro lines. Second, professional lines run in differential, or balanced, configuration. In a single-ended line, the signal travels down one conductor and returns along a shield. This is the simplest form of audio transmission, since it is essentially the same AC circuit you learned about in high-school physics. The problem here is that any noise or interference that creeps into the line will simply get added to the signal and you’ll be stuck with it. In a differential line, there are three conductors. A shield, a normal “hot” lead, and a third lead called the “cold” or “inverting” lead, which carries a 180-degree inverted copy of the hot lead. Any interference that creeps into the cable thus affects both the hot and cold leads equally.
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